A pneumatic tire, in which plural main grooves extending in a tire circumferential direction are formed in a tread and plural parallel ribs are formed by the main grooves in a tire width direction, has a small rolling resistance and is favored in general. However, such a pneumatic tire has a problem in that a so-called shoulder rib on an outer side of the tire in the tire width direction hardly comes into contact with the ground and a ground contact pressure of the shoulder rib tends to be non-uniform. When the ground contact pressure of the shoulder rib is not uniform, a braking performance may not be sufficiently exhibited.
In addition, in a pneumatic tire in which plural slits extending in the tire width direction are formed in the shoulder rib, it has been known that the inner ends of the slits in the tire width direction are terminated in the shoulder rib or the inner portions of these slits are so narrow as to be closed during the ground contact. When such a pneumatic tire is inflated, the inner portion of the shoulder rib in the tire width direction is hardly inflated and the outer portion of the shoulder rib in the tire width direction is likely to be inflated. Thus, the ground contact pressure within the shoulder rib tends to be non-uniform.
In this regard, as described in Japanese Unexamined Patent Publication No. 2006-168638, a pneumatic tire has been suggested, in which the entire portion of a shoulder rib (shoulder region) is made to protrude to the outside of a tire reference profile line of a center rib (center region) in a tire radial direction. In such a pneumatic tire, a shoulder rib and a center rib are brought into contact with the ground under substantially the seine ground contact pressures.